Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for MPLS VPN—L3VPN over GRE" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for MPLS VPN—L3VPN over GRE

Before you configure the MPLS VPN—L3VPN over GRE feature, ensure that your MPLS Virtual Private Network (VPN) is configured and working properly. See the Configuring MPLS Layer 3 VPNs module for information about setting up MPLS VPNs.

Ensure that the following routing protocols are configured and working properly:

Restrictions for MPLS VPN—L3VPN over GRE

•Quality of service (QoS) service policies configured on the tunnel interface; they are supported on the physical or subinterface

•GRE options: sequencing, checksum, and source route

•IPv6 GRE

•Advanced features such as Carrier Supporting Carrier (CSC) and Interautonomous System (Inter-AS)

Information About MPLS VPN—L3VPN over GRE

The MPLS VPN—L3VPN over GRE feature provides a mechanism for tunneling MPLS packets over non-MPLS networks.

MPLS VPN—L3VPN over GRE allows you to create a GRE tunnel across a non-MPLS network. The MPLS packets are encapsulated within the GRE tunnel packets, and the encapsulated packets traverse the non-MPLS network through the GRE tunnel. When GRE tunnel packets are received at the other side of the non-MPLS network, the GRE tunnel packet header is removed and the inner MPLS packet is forwarded to its final destination.

PE-to-PE Tunneling

The provider edge-to-provider edge (PE-to-PE) tunneling configuration provides a scalable way to connect multiple customer networks across a non-MPLS network. With this configuration, traffic that is destined to multiple customer networks is multiplexed through a single GRE tunnel.

Note A similar nonscalable alternative is to connect each customer network through separate GRE tunnels (for example, connecting one customer network for each GRE tunnel).

As shown in Figure 1, the PE routers assign VPN routing and forwarding (VRF) numbers to the customer edge (CE) routers on each side of the non-MPLS network.

The PE routers use routing protocols such as BGP, OSPF, or Routing Information Protocol (RIP) to learn about the IP networks behind the CE routers. The routes to the IP networks behind the CE routers are stored in the associated CE router's VRF routing table.

The PE router on one side of the non-MPLS network uses the routing protocols (that are operating within the non-MPLS network) to learn about the PE router on the other side of the non-MPLS network. The learned routes that are established between the PE routers are then stored in the main or default routing table.

The opposing PE router uses BGP to learn about the routes that are associated with the customer networks behind the PE routers. These learned routes are not known to the non-MPLS network.

For this example, BGP defines a static route to the BGP neighbor (the opposing PE router) through the GRE tunnel that spans the non-MPLS network. Because the routes that are learned by the BGP neighbor include the GRE tunnel next hop, all customer network traffic is sent using the GRE tunnel.

Figure 1 PE-to-PE Tunneling

P-to-PE Tunneling

As shown in Figure 2, the provider-to-provider edge (P-to-PE) tunneling configuration provides a way to connect a PE router (P1) to an MPLS segment (PE-2) across a non-MPLS network. In this configuration, MPLS traffic that is destined to the other side of the non-MPLS network is sent through a single GRE tunnel.

Figure 2 P-to-PE Tunneling

P-to-P Tunneling

As shown in Figure 3, the provider-to-provider (P-to-P) configuration provides a method of connecting two MPLS segments (P1 to P2) across a non-MPLS network. In this configuration, MPLS traffic that is destined to the other side of the non-MPLS network is sent through a single GRE tunnel.

RFCs

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Command Reference

Feature Information for MPLS VPN—L3VPN over GRE

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 1 Feature Information for MPLS VPN—L3VPN over GRE

Feature Name

Releases

Feature Information

MPLS VPN—L3VPN over GRE feature

The MPLS VPN—L3VPN over GRE feature provides a mechanism for tunneling Multiprotocol Label Switching (MPLS) packets over a non-MPLS network.

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